The present invention relates to an expansion system for a liquid crystal video display device of a matrix type, and more particularly to a liquid crystal display system in which a part of a video signal is displayed on a matrix display panel on an increased scale.
FIG. 1 is a block diagram showing a conventional liquid crystal video display device. Video signal is fed to a sync separator 1 and memory circuit 3. A control unit 2 operates to control a data electrode driver 4, scanning electrode driver 5, and memory circuit 3 in dependence on synchronizing signals separated by the sync separator 1. A liquid crystal display panel 8 has a plurality of scanning electrodes 6-1, 6-2 . . . 6-N and a plurality of data electrodes 7-1, 7-2 . . . 7-M. The number of scanning electrodes (N) is decided by the number of scanning lines in a field.
Referring to FIG. 2, a video signal 9 has 262 periods dependent on the number of scanning lines. A scanning electrode driving signal having a voltage which is obtained by 120 time-division multiplex drive method is sequentially applied to a selected scanning electrode during two horizontal scanning intervals of 2H (H is a period of one horizontal scanning interval). Accordingly, the selected scanning electrode (6-1) is applied with a scanning electrode drive signal during the scanning intervals (1) and (2), non-selected scanning electrodes (6-2) to (6-N) are applied with a scanning electrode non-drive signal. At the same time, data electrodes (7-1) to (7-M) are applied with data electrode drive signal or data electrode non-drive signal dependent on the selection in accordance with the video signal. During the next horizontal scanning intervals (3) and (4), the scanning electrode (6-2) is applied with a scanning electrode drive signal, and other electrodes are applied with a scanning electrode non-drive signal. At the same time, data electrodes (7-1) to (7-M) are applied with drive signal or non-drive signal. Similarly other scanning and data electrodes are sequentially applied with signals. During the intervals (239) and (240), the scanning electrode (6-N) is selected and one cycle completes in a field. At every vertical scanning interval, selection of the data electrodes is carried out in dependence on the video signal. Thus, picture is displayed on the display panel 8 in accordance with the video signal.
Referring to FIG. 3, a picture 10 on a CRT is displayed on the display panel 8 by the above described manner without expansion. Here, the expansion of the picture means that a part 11 of the picture 10 is expanded on the whole or a part of the display panel 8.
Explaining the expansion of the period between the intervals (120) and (239) of FIG. 2 (the expanded period is selected on demand), the picture data during the period are stored in the memory circuit 3 of FIG. 1. The stored picture data are displayed on the display panel 8 in accordance with the synchronizing signals in the same manner as the above described one.
In such a conventional system, since a memory is provided, the size of the display device is increased. Further, the device is expensive and decreases in responsibility.